This invention relates to a planetary transmission and more particularly to a power shift transmission having dual planetary gearsets with a brake and clutches for selectively shifting power paths through the transmission to provide three forward speeds and one reverse speed.
Vehicle transmissions used on tractors provide a plurality of forward speeds and at least one reverse speed. Because of the variation in draft load which is applied to the tractors it is desirable to have a means of shifting the transmission speed ratio up or shifting the transmission speed ratio down while the tractor is in motion. This is desirable because the draft load on the tractor varies with soil conditions, wheel traction, uneveness of the terrain. If the tractor were stopped to shift gears, it is possible the tractor will never be able to be started again because of the failure of traction particularly where the soil is soft and the traction may be scarcely adequate to keep the vehicle traveling. Accordingly, a vehicle transmission which can shift up or shift down while the vehicle is traveling will supply continuous power to the wheels and maintain the momentum of the tractor and allow the tractor to get over the area where the wheel slippage is at a maximum tolerable rate.
Accordingly, this invention provides a three speed transmission with three forward speeds and one reverse speed. The transmission is a power shift transmission in which the elements of the planetary gearsets may be selectively engaged or disengaged while the vehicle is in motion. Only one of the clutches or the brake is changed to provide a selectively different speed ratio of higher or lower gear ratio as desired. As the one clutch or brake is disengaged, another clutch or brake is engaged to provide smooth transition of power from the one clutch to the other clutch to increase or decrease the speed ratio of the gears in the transmission as desired. Accordingly, the vehicle transmission can be shifted to continue the forward movement of the vehicle without losing momentum and to provide continued power to maintain the drawbar traction as needed. The relative speed of adjacent clutch friction members is low so that the transition of power from one ratio to another does not cause roughness as the transmission is shifted from one clutch to another. A suitable pressure modulating means is provided to selectively engage one of the hydraulic actuators operating a brake or clutch while the other hydraulic actuator is disengaged.
The transmission is adapted for operation with a range transmission which may be a mechanically shifted transmission in series with the power shift transmission. In other words, a selected speed of the range transmission can be mechanically shifted while the vehicle is stationary and then the increase or decrease of the speed ratios in the power shift transmission can be shifted while the tractor is in motion.
It is an object of this invention to provide a dual planetary power shift transmission having three forward and one reverse speed.
It is another object of this invention to provide a dual planetary transmission for transmission of power through either or both of the planetary gearsets and selectively shift the transmission while the transmission is in operation.
It is a further object of this invention to provide a dual planetary power shift transmssion with an input shaft driving the ring gear of one planetary gearset and the sun gear of the other planetary gearset with selective output from the ring gear of one planetary gearset and the planetary carriers of the two planetary gearsets.
The objects of this invention are accomplished by providing two planetary gearsets having sun gears rotating on a common axis of rotation, each planetary gearset includes a sun gear, a ring gear and a plurality of planet gears with a planetary carrier. The sun gear of the first planetary gearset is connected to the transmission housing. The input shaft is rotatably mounted for rotation on the common axis with the sun gears of the planetary gearsets and is connected to the ring gear of the first planetary gearset and the sun gear of the second planetary gearset. A torque transmitting member rotates about said common axis and can be selectively braked to the transmission housing or selectively clutched to the planetary carrier of the first planetary gearset to transmit power to the planetary carrier of the second planetary gearset or the output shaft. The output shaft rotates about said common axis and is carried on the clutch carrier. The clutch carrier carries clutches for selective engagement with the ring gear of the second planetary gearset and the planetary carrier of the second planetary gearset to transmit power to the output shaft. Accordingly, selective power shifting provides braking or clutching of the torque transmitting member and clutching of the clutch carrier with transition of no more than one of the brakes or clutches to vary the speed ratio and provide three forward and one reverse speed of the transmission.